Grinding cam lobes on a cam shaft has usually been achieved by a grinding wheel, which grinds each cam in sequence. In some instances, by resort to complex mechanical machines with two grinding heads, a pair of cams may be ground concurrently.
In response to the needs of automotive manufacturers, in particular, efforts have been made to devise and develop, a reliable grinding machine that will grind, simultaneously, a number of or all of the cams, or lobes, on a camshaft. Since camshafts are a costly and complex article of manufacture, and since the costs of manufacturing same are significant, diverse approaches have been considered to move, technically, beyond the well known techniques relying upon grinding wheels.
One alternative approach has focused upon the use of abrasive grinding belts in lieu of the conventional grinding wheel. Such approach has considerable potential, for several belts may be utilized, in side-by-side relationship, to grind the several lobes on a camshaft simultaneously. Also, the belts, if mass-produced, will be much lower in cost, and can be discarded, after usage for an extended period of time.
Abrasive grinding belts may have been initially used in Italy ten or more years ago to grind camshafts as illustrated in U.S. Pat. No. 4,175,358, granted Nov. 27, 1979, to Ido Boscheri, which discloses a plunge grinding machine employing several abrasive belts to simultaneously grind all of the cams which are present on a timing shaft for an engine. Such grinding machine includes a massive baseplate (10) which carries a table (12) which can be reciprocated (by jacks 13) with respect to the baseplate, a tail stock and head stock mounted on the table and adapted to support the camshaft (19) to be ground, and a stationary crosspiece (22) carrying a plurality of machining units. Each machining unit comprises a supporting member (31), front and rear heads (32, 33), an abrasive belt (36), jack (43), etc. that are driven by a sensing roller (42) operatively associated with a pattern piece (18) from which the workpiece (cam) to be ground is copied. Separate drive motors (15, 25) are connected through appropriate gear transmissions and couplings so that the workpiece to be ground, and the pattern piece, are rotated in the proper phase relationship.
U.S. Pat. No. 4,833,834, granted May 30, 1989, to Henry B. Patterson et al, discloses several embodiments of multiple belt camshaft grinding machines. Each grinding machine has several grinding belts (28) and a drive (such as main drive pulley 30) therefor, and contouring shoes (35) and support members (pushrods 43) carried on a feed table (12) for separate control of cam contouring and grinding feed rate. The camshaft workpiece (20) is carried on a fixed axis by a table (16) providing axial motion for belt wear balancing oscillation. The grinding operations may be controlled by master cams, as in the embodiment of FIGS. 1 and 2, or may be numerically controlled, as in the embodiments of FIGS. 3 and 6-10.
U.S. Pat. No. 4,945,683, granted Aug. 7, 1990 to James D. Phillips, discloses an apparatus for grinding, to a predetermined contour, a plurality of eccentric cams (L) on a camshaft (W). The apparatus comprises several abrasive belts (58) supported adjacent the cam shaft for linear movement, such that the belts grind the peripheries of the cams (as shown in FIGS. 1 and 8). The belts are guided along a variable path, according to the cam contour desired, by shoes (72) engaging the belts at their point of contact with the cams. The shoes are mounted on actuators (76) powered by motor units (78) controlled by CNC controllers. Each belt passes through a coolant distributor (130) so that coolant saturates each belt and conditions same for better abrading action. The pressure of fluid within each distributor causes the belt to flex, and compensates for the tendency of the belt to stretch as the shoe 72 moves in and out.
U.S. Pat. No. 5,142,827, granted Sep. 1, 1992, to James D. Phillips, discloses a crank pin grinder employing multiple abrasive belts.
The latter three patents reflect the increasing interest in grinding machines employing several abrasive belts, side by side, to grind all of the surfaces, on a workpiece. The market potential available to the manufacturer of a commercially acceptable grinding machine that employs abrasive grinding belts may be significant.
While a limited number of grinding machines using abrasive belts have been manufactured, and used commercially in the past decade, the costs of designing, operating, and maintaining such multiple belt machines, have proven to be a significant economic burden. The abrasive belts have broken frequently, or have deteriorated rapidly to produce ground surfaces that fall outside acceptable tolerances.
These aforedescribed prior art grinding machines do not provide for effective disposition of the respective grinding belts to insure accurate and optimum grinding; for selective adjustability of the belt drive and effective and efficient control of belt positioning to maximize belt life and effectiveness; or for utilization of similar assemblies at multiple locations to reduce manufacturing and maintenance costs. These, and other, shortcomings of known belt grinding machines have inhibited the widespread acceptance of grinding machines employing multiple abrasive belts, to date. Problems have also been encountered in aligning the multiple belts relative to one another, in both the horizontal, and vertical, planes. Also, the debris generated by the grinding machine has attacked the drive motors, used in the component subassemblies, and has necessitated the use of costly, sealed drive motors at various locations.